Re: [Gretl-devel] C-isms in hansl

On Sun, 18 Sep 2016, Sven Schreiber wrote: First off, the genetic difference between "print" and "eval" is historical: "print" is an ancient command (originally used only for printing series), while "eval" is an offshoot of what was once our "new genr" apparatus (a proper recursive descent parser). "New genr" has been around for many years now but it long postdates "print". If these respective histories were the only real difference between the two commands, there would surely be a case for merging them. However, I don't think history is the only relevant difference. While some usages of the two are pretty much equivalent, each command offers generality in its own specific dimension. In the case of "print" you can print the values of multiple objects: you can put the names of as many objects as you like (simply space-separated) on a "print" command line. In the case of "eval" you are allowed just one expression on the command line, but it does not have to be the name of an existing object; it can be as complex as you like, as in eval (y - X*inv(X'X)*X'y)'(y - X*inv(X'X)*X'y) (not a smart usage, but never mind). It seems to me these extensions cannot be combined. An argument-array which simply lists a bunch of objects of arbitrary type is fine for "print" but is not something that's going to work with "eval", which is inherently looking for something that makes syntactical sense -- something that would be OK on the right-hand side of an assignment, except that you don't care to assign the result to anything. Even in very basic usage, there's a difference which I sometimes find useful (in the sense of having a reason to prefer one or the other command, depending on the context): "eval" simply dumps the result, while "print" may add some extra information (e.g. in the matrix case, where the name and dimensions of the matrix are displayed). Sometimes I'd like to see the extra info, sometimes not. Allin